Economic Prospects and Legal Aspects
Hinge belts between shelves and basins are sought by petroleum explorationists as preferred sites of hydrocarbon accumulation. Shelf-slope breaks between continents and oceans are the largest and most durable of such belts. They may or may not be associated with plate boundaries. Ancient shelf-slope breaks of this order are not, however, especially favorable sites for hydrocarbon accumulation. Hinge belts having all the structural and lithological hallmarks of true shelf-slope breaks may, however, be developed within restricted or interior basins, or they may face such basins rather than facing open oceans. These inward-facing breaks are highly favorable sites for hydrocarbon accumulation, although it is commonly impossible to demonstrate more than general coincidence between the accumulations and the breaks.
Shelf-slope breaks providing control for hydrocarbon accumulations in interior basins may survive with little or no deformation, as in the Permian Basin. Those forming parts of the margins of extensional ocean basins may similarly survive the stabilization of their basins, as along the Atlantic Ocean margin. Those within convergent margins become deformed or concealed by incorporation into orogenic belts like those along the Tethyan Sea margins. Three principal source-reservoir lithological associations are considered: carbonate-evaporite, mixed carbonate and clastic, and wholly clastic. The second is the most likely to result in large hydrocarbon accumulations in immediate proximity to the breaks; the last is least likely to do so. Notable examples described herein are: (1) the inner foothills fields of Iran and Iraq and the Golden Lane-Reforma-Campeche fields of Mexico, representing the carbonate-evaporite association; (2) the Permian basin, the Cretaceous of the U.S. outer Gulf Coast, and the fields of the Brazilian Campos and Southeast China Sea basins, representing mixed lithological associations; (3) the Arkoma and Upper Assam Valley basins as deformed representatives; and (4) the northwest Australian shelf and the Texas Gulf Coast Eocene breakover as undeformed representatives of the clastic facies association.
Figures & Tables
The shelfbreak is that point where the first major change in gradient occurs on the outermost edge of the continental shelf. Although this environment delimits the boundary between two principal and well-defined provinces, the continental shelf and slope - and thus is of the first order of importance on continental margins - it has received surprisingly little specific attention in either modern oceans or in the rock record. This volume, the first compendium dedicated specifically to the shelfbreak, was derived from an SEPM Research Symposium convened at the joint Annual Meeting of SEPM and AAPG on June 2, 1981. The material is organized in a manner to illustrate examples of the shelfbreak in both modern oceans and the rock record.